How Does Resistance Spot Welding Compare with Laser Welding and Other Welding Methods?
Resistance spot welding may be an older method, but it is still one of the best for welding many industrial parts, especially in the high-volume production stage. Used extensively in automotive and electronic parts manufacturing, resistance spot welding basically is sandwiching two metals to be welded in between an “outer” sandwich of two electrodes and cycling electrical current through this sandwich to weld the two metals.
While the use of laser welding and ultrasonic welding is certainly growing, the machines required are expensive and there are major limitations to the thickness of materials that can be joined together using those methods. In addition, there is one important advantage of resistance spot welding — that is, you get the clamping for free.
Spot Welding Includes Clamping
Clamping refers to the requirement that the metals being welded need to be held together, preferably pressed together to maximize contact, and held in an exact position with no shifting or movement before or during the welding process. By its very design, resistance spot welding utilizes two electrodes pressing down on two work pieces that will ultimately be welded together. This necessary clamping process, which is used to achieve the metal-to-metal surface contact and pressure needed to make for the best weld possible, is simply inherent in spot welding. Clamping is supplemental or secondary when using a technique such as laser or ultrasonic welding — a separate function that must occur simultaneously to the welding technique itself, complicating the entire welding process.
When welding at low volume, it is of course possible to accommodate the additional clamping requirement of laser or ultrasonic welding. However, when the goal is high-volume production at the lowest cost possible, traditional resistance spot welding remains a significant and beneficial production method — clamping included!
What are considered to be high-volume production applications where resistance spot welding is beneficial? Some common examples include motor terminals, coil terminal, relay terminals, electronic guns, and certain types of halogen lamp assembly.
Spot Welding Adapts to Complexity
One of our specialties, and a specific example of a great application for resistance spot welding, is the wire harness terminal. Just think of all the wire harnesses that are inside an automobile. A car has come to be, and is ever increasingly, a remarkable communication device in and of itself. In the old days, it was as simple as turning a knob to send a signal to the ends of the car to communicate the desire to turn the headlights on/off or indicate a turn. Today, your vehicle is communicating with itself in ever more complex ways, and that is before even beginning to communicate with the outside world.
These days there are literally thousands of connections that need to be made inside a car, and tens of thousands in modern hybrid vehicles. And as the complexity grows, the number of connections grows while the diameter of the wires shrinks. This in turn has caused so-called old-fashioned welding to adapt, resulting in the specialized *micro spot welding techniques* that are utilized to create the fine connections required for the complexity of today’s automobile wiring.
Added Advantages in How the Electrodes Are Bonded
Of course, there are also challenges in resistance spot welding. For example, there can be inconsistent bonding quality due to pores in the bonded section of an electrode, reducing the bonding area to 60-80%. In addition, the on-off cycling between temperatures of 1200°C and 500°C can cause heat load that consumes the electrode.
However, many of these challenges are addressed through advances such as the *non-defective bonding (NDB) method* used to produce electrode assemblies made from tungsten, molybdenum and their alloys. An NDB electrode has no filler between the shaft and the electrode tip, creating a bonded area with almost 100% and producing a stronger and more consistent weld between the work pieces. In addition, an NDB electrode optimizes thermal cycling, to reduce heat load and electrode consumption.
The additional challenges and solutions are beyond the scope of this blog and are a good topic for another time. However, in the meantime, if you’d like to learn more about the NDB method and its advantages in the manufacture of welding electrodes, you can download our free technical paper on the non-defective bonding of resistance spot welding electrodes.